Singh-Rachford Tanya N, Lott Joseph, Weder Christoph, Castellano Felix N
Department of Chemistry and Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio, 43403, USA.
J Am Chem Soc. 2009 Aug 26;131(33):12007-14. doi: 10.1021/ja904696n.
The upconverting properties of a dye cocktail composed of palladium(II) octaethylporphyrin (PdOEP, triplet sensitizer) and 9,10-diphenylanthracene (DPA, triplet acceptor/annihilator) were investigated as a function of temperature in several low glass transition temperature (T(g)) polymer hosts including an ethyleneoxide-epichlorohydrin copolymer (EO-EPI) and the polyurethanes Texin 270, Texin 285, and Tecoflex EG-80A. Selective excitation of PdOEP at 544 nm in the presence of DPA in these materials resulted in anti-Stokes blue emission from DPA, a consequence of sensitized triplet-triplet annihilation (TTA) photochemistry, confirmed by the quadratic dependence of the upconverted fluorescence intensity with respect to incident light power. The upconversion process was completely suppressed by cooling a PdOEP/DPA blend film to below the T(g) of the respective polymer. However, the blue emission was clearly visible by the naked eye upon heating these films to room temperature (290 K). Subsequently, the upconverted emission intensity increased with increasing temperature and was found to be completely reversible upon several heating and cooling cycles provided the temperature remained below 400 K. Heating samples above this temperature resulted in unrecoverable failure of the material to produce upconverted photons. The phosphorescence intensity decay of PdOEP in the polymer host, Tecoflex EG-80A, adequately fits to a sum of two exponential functions as well as the Kohlrausch-Williams-Watts (KWW) stretched exponential model. Increasing the temperature of the film increases the complexity and heterogeneity of the system as evidenced by the lower beta values obtained from the KWW model as the temperature increases.
研究了由钯（II）八乙基卟啉（PdOEP，三重态敏化剂）和9,10 - 二苯基蒽（DPA，三重态受体/湮灭剂）组成的染料混合物在几种低玻璃化转变温度（T(g)）聚合物基质中的上转换特性，这些聚合物基质包括环氧乙烷 - 环氧氯丙烷共聚物（EO - EPI）以及聚氨酯Texin 270、Texin 285和Tecoflex EG - 80A。在这些材料中，在DPA存在下于544 nm处对PdOEP进行选择性激发，导致DPA产生反斯托克斯蓝光发射，这是敏化三重态 - 三重态湮灭（TTA）光化学的结果，上转换荧光强度对入射光功率的二次依赖性证实了这一点。通过将PdOEP / DPA共混膜冷却至各自聚合物的T(g)以下，上转换过程被完全抑制。然而，将这些膜加热至室温（290 K）时，肉眼可清晰看到蓝光发射。随后，上转换发射强度随温度升高而增加，并且发现在温度保持低于400 K的情况下，经过几次加热和冷却循环后，该过程是完全可逆的。将样品加热到高于此温度会导致材料无法产生上转换光子且无法恢复。聚合物基质Tecoflex EG - 80A中PdOEP的磷光强度衰减很好地拟合为两个指数函数之和以及科尔劳施 - 威廉姆斯 - 瓦茨（KWW）拉伸指数模型。薄膜温度升高会增加系统的复杂性和不均匀性，这可通过随着温度升高从KWW模型获得的较低β值得到证明。
